Oh I don't know -- how about the testimony of those who have had alien encounters ?
Unexplained pregnancies ? Scoop marks ? And the occasional radiation burns & sickness ?
The many 'missing time' reports by individuals -- or do you think they were all liars, who have gone mental ?
The numerous cattle mutilations that have cost ranchers many thousands of dollars ?
The circular landing marks in yards where grass will no longer grow ?
The numerous unexplained lights videoed performing non-accepted physics, in silence ?
The top secret government reports on 'UFO' cases ?
The changing cover-up stories on UFOs ?
No matter what physical evidence there is, the die-hard skeptics will find a way to ignore it.